The typical steam turbine-generator consists of multiple shaft segments having coupling collars which are coupled together to form a single rotating shaft. During turbine outages, maintenance personnel uncouple and remove one or more shaft segments for inspection. After uncoupling and prior to removal, the alignment of each turbine shaft segment is measured. During reassembly, the alignment between couplings is once again measured and compared to the original measurement or manufacturer's specifications to ensure that the shaft will be properly aligned. If alignment corrections are necessary, additional alignment measurements follow after each correction is made.
Shaft alignment measurements, more familiarly referred to as "coupling alignment checks", are a standardized sequence of rotational steps measuring the parallel and angular misalignment between two couplings. These steps include: temporarily connecting a pair of adjacent shaft segments; turning the pair of shaft segments several times to remove sag; rotating the shaft segments in 90 degree intervals; stopping after each interval to take a reading; and repeating the 90 turning process until a minimum of two full rotations is achieved. In total, for one alignment check, a minimum of 8 starts and stops is required to complete two rotations of the shafts.
Each shaft segment is very large and may weight up to 320,000 pounds. In order to connect and rotate the large shafts, barstock is inserted through aligned bolt holes of adjacent couplings and a turning force is applied by, for example, an overhead crane. The barstock temporarily connects the couplings during the rotation phase so that the turning force applied to one shaft segment is transmitted to the adjacent shaft segment. After each 90 degree rotation, the shaft segments must be disconnected to conduct an alignment check.
To disconnect the shaft segments, rotation is stopped and the barstock removed. Since the shafts are extremely heavy, the barstock typically binds in the bolt holes due to distortion (bending) of the barstock during rotation. Removing the barstock to make an alignment check is inhibited since this "torqued" condition remains in the bent barstock even when the turning force is removed. In order to relieve this "torqued" condition, the barstock must be loosened within the clearance of its hole. Loosening the barstock is extremely difficult and requires that one of the shaft segments be rotated in a reverse direction relative to the other.
Currently, several methods exist for applying the turning force required during coupling alignment checks. The most commonly used method is the combined use of a crane, a lifting cable, and round pin. The round pin is inserted halfway into one of the empty coupling bolt holes and the crane cable is looped over the free end of the round pin. The shaft or shaft(s) are then rotated a small amount by pulling the pin upward with the crane. Full rotation is achieved by relocating the pin in different bolt holes around the circumference of the shaft collar and pulling with the crane. This process is normally used for turning one shaft individually or, when used in conjunction with the aforementioned barstock connection, can be used to turn two shafts at the same time. However, as more shaft units are connected using barstock and turned in this manner, the load capacity of a single crane is challenged. As a result, a second pin and overhead crane must be used in conjunction with the first. This situation is undesirable since a complete alignment check may typically take up to 8 hours to perform, during which time two maintenance cranes are occupied.
As an alternative to using maintenance cranes, the already existing manufacturer-supplied turning gear may be used to provide the necessary turning force. The turning gear consists of a motor, speed reducer, and a large drive gear permanently attached to one of the shafts. During coupling checks, when barstock is inserted into any unbolted couplings, the turning gear will drive all the shaft segments at a very slow speed. Using the turning gear eliminates the need to use maintenance cranes; however, the turning gear does not alleviate the barstock binding problems described above.
Therefore, it would be desirable to provide an alignment tool which is constructed to temporarily connect, and quickly and easily disconnect adjacent shaft segments without becoming bound in the coupling bolt holes.
With the recent introduction of laser alignment technology, it has became absolutely necessary to maintain the clock position of the two couplings halves within seconds of arc. The barstock connection method cannot maintain the tight clocking relationship required of lasers due to the angular slippage between the couplings which occurs due to barstock bending.
Therefore, it would also be desirable to provide an alignment tool which maintains the relative angular position between the two shaft segments during the rotation phase of an alignment check.
When the large shaft segments are bolted together during initial assembly, it is often found that the axes of the shaft segments are not concentric. If the axes are not concentric, one shaft segment will "wobble" in relationship to the other during rotation causing turbine shaft vibration. To minimize turbine shaft vibration, the coupling collars should be bolted together as concentric as possible. This task, however, is not easy due to the extreme weight and size of each shaft segment.
In the prior art, adjusting coupling collar concentricity usually requires numerous hours of trial and error adjustments to the concentric (axial) alignment by loosening the connection bolts, hydraulically jacking one shaft segment relative to another, and then tightening the connection bolts. This is an inefficient and strenuous technique.
Another known method of correcting coupling concentricity involves jacking screw arrangements made to fit on the periphery of the coupling collars. While this technique is more efficient than the trial-by-error technique described above, it is also strenuous and time consuming, and requires expensive and bulky specialized tooling.
Therefore it would be desirable to provide an alignment tool which jacks one shaft segment relative to the other to achieve coupling collar concentricity in the shaft.